Controlling flow of fluidized solids



Feb. 23, 1954 R. PYZEL 2,670,193

CONTROLLING FLow 0F FLUIDIZED soLIns Filed Ma'y 9, 1949 INVENTOR. ROBERT PYzEL Hyg.

ATTORNEYS I ordinarily employed in the production oi hydraulic cement which requires a substantially lower expenditure of fuel than previous methods and which produces a cement product of greater uniformity than the product of previous processes. It is the general object of the invention to provide an improved process for reacting oxides of metals of group II, particularly alkaline earths, with oxides of metals of groups III and EV, such as silica and alumina, under conditions requiring the expenditure of a minimum amount of fuel and which facilitate the formation of a highly uniform product. Other objects and advantages of the invention will be apparent from the iollowing description.

1n accordance with the improved process of this invention the raw materials are formed into ai line powder, which may be nner than the powder previously employed in the rotary kiln method, and the powder is subjected to reaction conditions in a reactor while being maintained in a relatively dense pseudo-liquid condition in the reactor by the passage oi a gas upwardly through the powder mass at the proper velocity. The

powdered raw material may be charged to the l reactor in the chemical form in which it is customarily charged to a rotary kiln or the powdered raw material may be subjected to a preliminary burning in a separate zone to convert the calcium carbonate to calcium oxide.

rlhe heat necessary to sustain the reaction may be supplied with the stream oi gas, or fuel may be introduced directly into the fiuidized powdered mass and burned therein to provide the necessary heat. It is more economical of heat and conducive to the preparation oi a uniform product to subject the raw material to a preliminary treatment in a separate chamber to convert the calcium carbonate to calcium oxide. It is characteristic of this invention that the reaction Zone is maintained at a substantially uniform temperature throughout as a result of the circulation of the powdered particles throughout the fluidized mass of reactants. Consequently it is preferable to convert the calcium carbonate to calcium oxide in a separate preliminary treatment since this operation is best carried out at a temperature considerably lower than the temperature necessary ior reacting the calcium oxide with silica and alumina to produce the hydraulic product.

While such separate preliminary treatment is necessary only for that portion of the raiv material containing calcium carbonate it will be found convenient ordinarily to Subject the whole raw material to such preliminary treatment, since calcium carbonate ordinarily comprises the greater part of the raw material.

In accorda-nce with the improved process the finely divided raw material, which may or may not have been treated previously to convert the carbonate to the oxide, is suspended in the reactor in an upwardly flowing gas stream as a dense, pseudo-liquid turbulent mass in which the powderl particles circulate at a high rate to produce intimate mixing of the mass ci reactants. The gas stream is passed upwardly through the mass at a velocity which is suicient to maintain the reactants substantially in suspension in the gas stream. rEhe velocity oi the gas stream is maintained sui'liciently low to maintain the greater part of the mass of reactants in a pseudo-liquid condition in which it exhibits many of the properties of a true liquid, particularly as to flowability and density. At the same time the velocity is maintained sufficiently high to produce in the imply any movement of the mass as a whole along 'A portion of the the path of ilow of the gas stream. The mass of iinely divided reactants is suspended in the gas stream but not entrained therein, although a suspended solid may be carried away from the dense fluidized mass by becoming entrained in the gas stream emerging from the dense pseudo-liquid mass.

`The gas mixture is introduced into the reactor through an inlet in the bottom thereof whereby the gas stream passes upwardly through the mass of reactants to be maintained in a iluidized condition. Conveniently the inlet comprises one or more connections Whose aggregate cross-sectional area is substantially less than the corresponding dimension of the space in which the iuidized mass of reactants is to be maintained. The gas stream thus passes into the reactor at a relatively high velocity which prevents the passage of solids out of the reactor against the entering gas stream.

Inside the reactor the velocity of the gas stream decreases to the rate necessary to produce the desired degree of uidization of the mass oi reactants. For convenience the velocity of the gas stream in the reactor is given in terms of the theoretical velocity of the gas stream through an empty reactor and referred to hereafter as the superiicial velocity. It is evident, however, that the velocity of the gas stream decreases to the superficial velocity only if the reactor is suinciently larger than the volume of fluidized reactants to permit the maximum possible disengagement of the gas stream and the suspendded solids. As the concentration of nely divided solids in the iiuidized mass varies from a maximum at the bottom to a minimum at the top the linear velocity of the gas stream would normally decrease as it passes upwardly through the iiuidized mass, in the absence of reaction. The extent ioi the variation in the density of the luidized mass in the reactor is affected by the superficial velocity, the greatest variation in the density of the mass being observed at relatively high superficial velocity. rThe linear velocity of the gas stream may be aiected also by the change in volume of the gas stream, as it passes up through the reactor, as a result of an increase in temperature of the gas stream and as a result of the formation of gases by the reaction.

If the reactor is somewhat larger than the volume occupied by the fluidized mass of solid reactants the solids in the reactor appear to be distributed in two visually distinct phases. The iirst of these is the relatively dense, pseudo-liquid mass of fiuidized nely divided reactants, previously described, which occupies the lower portion of the reactor and comprises all but a minor proportion of the solids in the reactor. This phase is designated as the dense phase. The second phase, which occupies the upper part of the reactor, is a diiuse phase in which the concentration of solids is far less, and cfa different order of magnitude, than the average concentration in the dense phase. The diffuse phase may .be said tobe a disengaging zone in which the solids: liftedfzabovesthe denserphasetzby; thefsas streami` arefidisengagediathetetrcm @tof fthetextexttthat .suchsolids vare present inexcess :ofithe lcarry;- ingr-.capacitymfftheasfrstreamvat theilminimumvelocity reached 'byffthe: Afgasfff stream/t im the rre-v actorv Between the ydensefphase of'fhighf-concene; trationvv andsthe diuseel phase.- of; .low :concentrate tion :there is airelativelymarrowzone in Whichfthe concentration' fotsol-ids :changes la-'rshont sspace from the high-concentrationoithe, densebhase to thefrrlow-concentrationfroi the fdiiuseaphase. This zone-:hasthefappearance offen interface :hee--l tween two -yisuallyidistinct phases.` .y

While=:theinyentioneincludes i Witlziin'iits-y :scope the-usefof reactants of a-.suciently-jlargefparticle size such; -that :substantiallynof part for. 4the ree:v actantsfis -fcarried-` `by entr aimaient-1in'.i theagas; streamifat-the imaximum superficiali-velocity," the preferred method :of operation involves ordinarily the fusefof nely-,divided-.reactants and Aoperating conditions suchgth'at agportion offfthereactants is V:carried by entrainment 1in the gas-stream/yat the superficial velocity, This results from Ithe fact that nelydivided reactants =areldesirable as presenting aggreater ratio of surface to volume and, Ithus affording. the. maximum eiciencyf-'of reaction and maximum heat transfer 'between particles, and -fromf-the further fact that sufficient mixingof the fmass of nely .divided reactants ordinarily requires the 'useiof :superficial velocities Which-entraina portion of :the nelydividedsolids in the gas stream. In this preferred method of operationmcressettlingris not suicient ato disengage all the Jsolids -from the ggas streamA emerging from-the f 'dense phase -infthe reactor.` Hence u'it' may :be lnecessaryo` provide-,means tor separate entrained lsolids from;-,the1gas fstream emerging fromthe reactor:

The gasstream is withdraw-n fr omzthertoplof the lreactor througihffan exit-Which is ordinarily ofrsubstantially smaller crosse-sectionalareafthanthe reactor.;` Thisprovdes afhighfivelocityoutlet for the gaswhich is surrounded, byi-fan area-:in which :the-gasl velocityvacceleratesnl Thefnearerthis :zone "of acceleratingigasl velocity wisfto thedense phase #the greater :is-theI conce'titration fof solidsin'the gaspstream entering thefzone and the fgreater is the vquantity :of-solids' which-is' cariried out j-ofA :the ;reactor in theexit :gas- :stream: This :quantity approaches-the carrying capacity of vthefhighvelocity :ex-it ,fgasfstream when ,-it aisdesired f to main-tain the ,upperelevel lof, thesdense' phasefin the rvicinity :cfs the :zonezof 'accelerating velocity.:`r Infthe preferredmethodnfoperation; however, fthe reactor isamade ysufciently larger than the required volume of the dense=uidizedf mass ofv solidsrto providefa. relatively large diu'se phase fin which substantial: disengagement-fof sol-ids `from theifgaswstream .loccursiby Ymere Settling.i

The operation is:initiated,fby-ichargingnthe re-l actor withfa quantitycofanely:divided scrlidere-uy actants-fwhich itis :expected iw-ill be :equivalent to. the rmass :of hscrlids'A maintained in the :reactor inthe idense'.pha'se-.` 'Thereafter fthelapassage' ofv the gasstream'I into the greactors-Yand upwardly through fthe- :mass of solids iis -initiateld ati the velocity "whichruidizes theurmassfxil e.; converts tionffinvolving highly-turbulent @Infoticmzeof'v `.the particles..- Alternatively thel highlyturbulent' pseudo-liquidf phases mayb4 bet-r-estalilished.svin the :reactor i finitially byfiowing lithegasifstream through a substantially-empty reactorandschar'g- It* actoratarreteareatenthananeiearrrinsfcapaeityf offithe: gastream at the fsuperiiciai veloeityrime posed-byethendimensions; theffreactori Asffae result :of -thiseexcess `loadm 01- the-n gas estream the desired dense phase is graduallyrbuiltfupy-finthe reactor.: When-the height :of the dense phase inrthefreactorreaches the desired level theintroy ductienV of'v reactants iintof'thereactorfis carried onat a freduced rate orfisffstcppedgiin accordance wxitlrV ithe desired @methodeof operationy iff-,thereactantszzcharged-to`the reactoirare subistantialiyf-ree of carbon-atesifwhereby there-fis -no necessity for conversion foffcarbonates to s'oxidesin thereactorfthesnet heat: effect :offfthe@desiredfre -l actantsy risf fexotherrnic.`fv In :that-@case` it; :is -fnec'el essaryfonlyi toheat the reaction-mass ftor aftem pera-tureaat :which reactiontistinitiated. .There-. after the :heat 'fof'freactfidnr must` :be 1l:absorbed-:ytc avoid. foyerheatingff-the -massfof freac-tagntsf The heat ofareaction :may bezfabsorbed byg the.- gas. stream and the vsci-idrfreactantsf` VWflsliclfi fmayyfbe introducedy into :thefreaotor at temperatures :substantially l lower than,` the reaction temperature level and which are necessarily lWithdrawn.from the 'rreactorat approximately fthereactionyftemi-r per'ature Vvlevel. It is aefeature fof-v y:the-improved method -of `operation'.-,thatfthefreaction Amass-ismaintained `'substantiallysat1--a iuniform tempera-1 ture regardless of the heatingiandpooling-means appliedv to @it andregardless of;the,introduction` and withdrawal of isolid reactantsand gast, It is necessary .only to balance: the thea-t absorption by 'these ymeans against the -fzexothermic heat; of,` reaction yand any vsupplementaryheatingavmeans to maintain the Ientire iiuidized massrof reactants at axdesired uniform reaction-temperature :level:

If :the ,reactants-,charge'd'feto the -reaotor ,f contain a substantial' proportionfof carloonates,l whereby it isA necessary .toiconvert such carbonates to oxide in vthe reactor y*with -the ,-,evolutioniaoff carbon dioxide the net heatnectsofthe reactions may beendothermiczv,l In-fthat `case-"i1: isfnecessary :continuously .-to supply substantialqfheatieto the reactor tofmaintainthe :fluid-ized? mass of fre-` actants 'atthe desired reacticntem'perature level.A To supplyheat' ',to'the reaction, or to eiect the preliminary heating of the `reaction mass-fto the reaction temperature, any'suitable heating ,fmeans may be employed;A 4Conveniently fuel maybe-inf;v jecited directly Ainto *the-reactor' and. burned bymeans `of `oxygen' fin the agas j stream; i `Suchv fuel may be in the-form fof ia -fcombus'tiblegaswfsuchas natural f gas, a ,-oombustiblefliquid, such :as fpee' troleumf oil, for finely xdividedfso1ids,fsuch 1 as coal or coke.` Alternatively 4comhustion may .beecaireried zout-fin.; a separate chamber:ffrcuriV which f the hot `vgases pass into. the Vreactor to feiect simul-v taneous aerationfand heating 'otithe massz The; use of nely divided solids:injected:directlyiintcl the freactorf, is 'an f eiicientf .heating :meansrintoperations i which A'the ia-sh iresulting insuchzcomff bustion fcan Abe tolera-ted.1inffthe prodc-ti:r 'Forsten-:

ample, nely divided coal, which may rbe'ina particle Asize approximating ithatifof'the reactants, isi intimately :mixed with the iuidized mass fas thewresult Fory =the Thigh fc-rculati'onf'rate. #of theI particles; thereofand# ist.: burnedcuniformly throughout the -uidizedirmassby fioxygen icon-J tained -n the :gasp-"stream `employed fon eectingf iuidizationi4 ln'this.aman-nerT uniform heating-,sof themass is eifectedr.`

The yuse. ofathe gas'fstream to feiectcombustibn as y'well-fas to eiect -faerationL-inti'oduces vfanotherf factor togovern thevolumeof asuchrgasfrintro-x amount of heating it may be necessary to employ a quantity of gas, such as air, in excess cf the minimum amount necessary to effect iiuidization, in order to supply suicient oxygen for combustion in the reactor.

rl`he mass of reactants may be maintained in the reactor at the desired reaction temperature without the addition or withdrawal of the reactants for a time suiilcient to effect desired reaction. Thereafter the product may be withdrawn from the reaction and replaced with fresh reactants. Preferably, however, a small proportion of the fluidized mass of reactants is withdrawn continuously from the reactor and continuously replaced with fresh reactants. This proportion is regulated to provide an average residence time sufficient to effect complete reaction whereby the material continuously withdrawn from the reactor consists substantially completely of the desired reaction product.

In accordance with a preferred modification of the invention raw materials comprising substantial proportions of carbonates are treated in two reaction stages. In this method of operation the reactants are introducedinto a first stage, maintained under the above described luidized conditions, in which the temperature is maintained at the level necessary to convert the carbonates to oxides. Since this reaction is highly endothermic it is necessary to supply a substantial quantity of fuel continuously to this stage. The product of this operation then passes to a second treating stage, corresponding to the reaction Zone described above, in which the huidized mass is maintained at the temperature necessary to form the desired cement product. As the reactions occurringr in thist stage are exothermic it is necessary to supply only a relatively small amount of heat to the reaction mass. The heat of reaction is absorbed in heating the entering reactants and gas stream.

To produce the turbulent pseudo-liquid condition in the dense phase it is desirable that at least a substantial proportion of the mass of reactants shall consist of particles whose free settling rate is less than the superficial velocity in the reactor, whereby such particles are capable of being entrained in the gas stream. The mass of reactants may consist advantageously of a mixture of particles varying in size from 40 to 400 microns (average diameter). However, particles of smaller or larger diameter may be present. rIhe gas stream may be charged to the reactor at a rate corresponding to a superficial velocity of 0.1 to 1G feet per second, depending upon the degree of turbulence desired and on the necessity for extra oxygen for combustion purposes to maintain a highly iiuidized mass of solids at a uniform temperature. A minimum superficial velocity of approximately 0.5 foot per second is necessary for most purposes and velocities between that gure and 1.5 feet per second will be found useful.

The gas employed for uidization may be any gas which does not contain ingredients which effect undesired reactions in the reactor. Ordinarily air is highly satisfactory as it is substantially non-reactive with the reactants and contains oxygen which may be used to support any desired combustion in the reactor. It is evident, however, that any suitable gas may be employed.

The invention includes within its scope a process arrangement for handling the raw material and the product in a manner which is most economcal of heat. .This may includethe provision of heat exchangers such as chambers in which the reactants are maintained in the nely divided fiuidized condition and through which the iinely divided solids now in a continuous or semi-continuous manner. This arrangement, and the improved process in general, will be described further and in more detail by reference to the accompanying drawing which is a diagrammatic representation of apparatus for carrying out one modication of the improved process.

Referring to the drawing a main reactor l is provided for carrying out the treatment of a i'luidiaed raw material substantially free of carbonates in the manner generally described above. A preliminary carbonate reactor 2 is provided for effecting a preliminary conversion of carbonates to oxides in the manner generally described above. A. preheater 3 is provided for preheating the raw material charged to the carbonate reactor by contact with waste gases from the latter. An economiser l is provided to preheat the gas stream charged to the main reactor, or to the carbonate reactor, by contact thereof with the hot product of the process. In the specie modification of the invention illustrated by the drawing preheater 3 and economizer d are operated in a manner to maintain the reactants or product in a. iiuidized condition. It will be understood, however, that this is not necessary in accomplishing the functions of these parts o the process and that any equivalent heat saving means may be employed.

The waste gas stream from carbonate reactor 2 passes through line ii to the bottom of preheater 3. The finely divided raw material, which may comprise a mixture of finely ground cement rock and clay or limestone, is introduced into prehea-ter t by any suitable method. The finely divided reaction mass may be charged directly into preheater 3 through a suitable opening (not shown) prior to initiating the passage of the gas stream therethrough or preheater 3 may be charged with reactants through line 6 which connects line 5 with a suitable supply source,

The finely divided reactants are supplied through line E to the gas stream passing through line 5 at the rate at which such solids can be carried by the gas stream upwardly into preheater 3. In this manner the formation of the dense fluidized mass is effected. When a sufficient volume of the dense phase has been produced in preheater 3 the rate of charging of fresh feed through line E is adjusted to correspond to the rate at which it is desired to transfer preheated raw material from preheater 3 to carbonate reactor 2.

The inely divided reactants are introduced through line 6 by any suitable means but preferably in the form of a mass which is maintained in a fiuidized condition. To assist in maintain-v ing this condition an aerating gas may be introduced into line 6 through line This aerating gas may be any suitable gas such as air 0r waste gas or steam and may pass either upwardly in line 6 or downwardly therein or in both directions. A valve 8 is provided in line 6 to regulate the rate at which solids are introduced into line 5 from line e. The section of line 5 between line 6 and preheater 3 may be enlarged in accordance with the increased volume resulting from the addition of solids and to obtain reduced velocity of the gas stream which may be desirable after the introduction of solids therein.

In preheater 3 the waste gas and the mass of raw materials is brought to a substantially uni-g,

.form temperature Tby g permitting ma. :isuflcient 'residence time' ofthe:solidsimpreheaten3; The :preheated rawizmaterialfsmay :be wit drawn from .preheater A53': in^ar1y-suitablev manner-.fand from any point thereof'fortransferktofcarbonate reactor. 2*.. Conveniently, however,..this lisf effected fbyf means voi.:a.- verticalstandpipe"9=whichextends upwardly. :into-1. preheater to2: a fheight'e substantially-below? the f-level of .the interfacea'at am. Standpipe-ff connects at. its: lower end' ywith 'line I Ithrough which hotrfgases.fromrreaetor-fI A.and .'eccnomizer"v 1..areg-v passed.-` into.: the: lower apartAv of .carbonate 1 reactor 1 42. .The .'fiuidized preheated raw materials flowvinto-i theaupper#endeofestand- :pipe S11-andv passdownwardly therethroughinto aline I I. '.'Theiow.-Y of such-\ solids through stand- .pipeSr may berregulatedf'and:assistedwby-.means .oftfaeratingigases introduced` through linef I2. -xA valve I3 `is; provided 'in standpipers to regulate the iow -of sol-ids:A into .line-1 I-I. Lina Iy I': is; suitably enlarged between standpipeffa andvcarbonatev-re- Yactor 2.

.If valve I3 seemsy to -Wearf-excessively becausefof .the temperature l of owing solids, its @control unctions. may be. eliminated vbyrsubstituting fa .xedz orifice: andxregulat'ing` the now .accordance with the method of the present invention, i.e..by varying thefintroduction offaeratingfgas .through vline I2. "However theneed. for this type ofsfa'controlf. is notso.: great at. the! relatively-low temperatures :in the;1preheater 3i as inthe ear- Abonate reactor 21andthe mainreactor .I.. The valvermay-L beretamedfbut'left fully IopenedyI/h-ile the orice=assumesthe:.contro1 functionsI 'during operation. .Inf thisr way,:.- the lvalve vmaywbe emf .ployedf-.on occasions-at: shutvoi -fora'exampler Abut 'sisrelievedsof the constant wearfwhich. idestroysrit. iT-he hot i-gases passing through; line; I I `vwill urtherfgpreheatthe :raw #material tto.' the temperature necessary-toaeffecti conversion of-:fcarbonates to oxide and may supply a part of the end'othermic'heat of reaction. The remainder `of-the' -heat 'of-reaction-is supplied by the vintro- 'duction-"ofifuel or"by other heatingmeans f in 'accordance withy the general methods described `above; The"introductionyof 4fuel directly finto `carbonate'rea-ctor Tbya' pipe line* or byascrew ccnveyeror "by lany lother means isfiridicated diagrammatically at I4. The volume of gas introducedinto carbonate"reactorz` through" line I I..-o1.dinarily is.somewhatgreater.thanthe: mini- -mumr necessary to: effectfluidization ofr'thef mass of reactantsthereinsince itisnecessary lordinarily'to supply additional oxygen te supporti-com.- zbustion of the.` fuel ssuppliedt-at-v M. .-.In:any1-case thezimass :of reactantsA in :carbonat reactor .2

sis' maintained:infa'` highly turbulent; condition; in

ywhich .theheat exchange between'ithe various :parts ofthewturbulent massris highly e-iicient :whereby the mass is. substantially at.Y a.- uniform temperature The' hot .-gases.-` pass from the 4top fof: carbonate-reactor. 21 through-line fvwhich .econ- .inects .'With; tlieabottomiV of.' preheater 3;- in which .thefwasteagases arer'contactedfwithincoming. fresh ,reed-asia heat: savings measure.

.,Asstandpipe I5;similarifinsoperationwtorstandrpipei9, :fis-A provided towithdraw"reactants.i from .carbonategreactor 2. 'sThe ratefoffwithfdrawal of reactants through standpipe'f I5 is adjusted` to .imaintainaianfaveragerresidencetime of there- :actants 'vini-.tirei carbonatefreactorzfsubstantially gneater: than the.timemecessaryttoreifectxthefreaaction. 'As...f.a :'-resulti the euromunt; withdrawn t5: fori-transferium :mainsta- 1.10 rateeof'- withdrawal; of reactantsx through .fstand- :pipe trisfadjusted also. to maintainan-.intertace `lI I5 :about :half Way .-up.- in= carbonate.v reactor fd. .This permits substantial ydisengagement obsolids from. thegasstream prior to. passage ot thelatter to line 5.

:It risy important that.the' ratef'of `Withdrasrahoi :the` down-flowing r solids.. be quickly ...and ...easily :Variable ateall .times vduring an-operating run.

#Since most valvesl would 4.be destroyed.: .atten a short .-jperiod.y in use with solids at .temperatures over. 2,0009 F., van: orifice t8.- is. provided. instead of a valve, and fioW iareg-ulated.` by. varyingthe .density of"thestandpipestream in: standpipe I5. The Valve :orice may bef determined byeither :making it: sufficiently-.small sothatftheminim-um `desired :flow is obtained -when the l:staizidlpipe v stream is at-a minimum. density, i.v e. aeration through piper- I vl" is at a-maximumconsistent-With fsatisfactoryoperation; cr, .if minimum..-f1o.w.is not critical, the orice maybedesignedfwithfrefference to: the maximum flow desired-by making -it suiciently'. large. to.- pass the. maximum .desired :flewY .whenythet standpipestream :is yat amaximum .density consistent `with satisfactory 1 operation, isz-e. when: aeration` through. pipe I'I is. -at-.a-mim- ..mum-.all=owable value.

4The lower end of `standpipe l--.connectswith line: I9 which extends from the.top ofteconomizer .4f to the bottom ofthefmain: reactor.- I... Through line I9 there. isintroducedlinto reacton4 Iitlaefgas stream necessary to. uidize-.the mass ycizsreactants. .This gas streamffandthe reactantsfintroatures' substantially lower than the reactiorrtem- 4perature level. :desired .in reactor I. .Howeverrthe .gas'stream and acconrpanyirrg reactants entering reactor I Vfreind-ine I9 are preheated 5to5 .theridesired reaction -temperat-ure by" the .highly turbnlent 'uidized massf of.. reactants-in reactor I, .whichl-ismaintained at the desired'reactiomtem- Aperature level by-.the.-exothe.rmic heat .of reactionf and by af smallf4:1,uantitypof-1 fuel introduced -throughiline Ma in a/.manner-.simiflartoithezsupply. offuel totherca-rbonate: reactorasdescribed above. .The exothermic: heat offreactiomandrthe requirements of the process as to volume offluid- .izing .-gasvandv quantity of? reactantsfcharged are such. thaty :ordinarily the Jentire: heatrofrreactibn v.-is.l.alc sorls ed yby thereactants and-iiuidizing .-gas introdueed'from line I9 intoreacton I.

The: reacticni product is i withdrawn N.continucuslyf from reactor' I throughaa'f-standpipefsthe .rata of lWithdrawal#being adj-ustedtto maintain the interface at. then desired'lleve'l-Tamd toprovi'de la holding timecffreactants 'reactorK Issub'stan- 'tial'lv greater'V than I the` time)v necessarytoe'ect the reaction; fThehot gases*front-reactor.r I lpass throughfline I I to-carbonatet'reactorrzz .Einel'l A:alsoi receives sa; 4economizer-JI. "This serves -tos'reducenthe temperaturei ofi the gas from reactorv I. to .'.a'a ilevelrmoze .suitable f forV transmission' to freactorsz. andralso .to-supplyfzthe.extraffoxygerr: necessarylto support 'combustioniirr react/cm2.

fStandpipe 20'? is :provided .with'aeratmgmeans at :2 If'- and an: -orice22,1Whichcoactrtotptovlde tflow.v regulation in .responseftorvariations inthe .supply Yof:.aerationrgas- The :outletiof oricef: 22 discharges into linef23-through 'Whichiairflor the prccessis-introducedfintotthe bottom-fonctionmizert. .-A.; compressor .24 is 'ftprcvidedrinzitine :2.3mm ,impose :the necessary pressure onitlfre system.4 The rhot"- prcdnctapasses downwa diy `thoroughristaridpipe;:2IJ5 intoaiinev Where... iii' partrof the gasesifemergirrgzfrom picked up by the air stream and carried into eoonomizer Il. In economizer 4 the uidized mass of the product is maintained to permit effective contact between the air and product. The quantity of air introduced` into the system through line 23 is regulated by the requirements of carbonate reactor 2 and reactor I. Since this requires a quantity of air which is greater than the amount necessary to fluidize the reactants in reactor I the preheated air emerging from the top of economizer 4 is divided between line I8 which passes to the bottom of reactor l and line 25 which connects with line I I The partially cooled product is withdrawn from economizer 4 in a uidized condition through standpipe 26 which is provided with aerating means 21 and a valve 28. This product may, if desired, be passed to a second economizer or other heat saving means. If desired, valve 28 may be replaced or augmented with an orifice as previously described.

The waste gas which passes from the system through line 29 at the top of preheater 3 may be treated for the recovery of solids entrained therein. suitably this gas is passed through separatory means such as cyclone separators and the solids thus separated are returned to preheater 3. Conveniently such separating means may be placed within preheater 3 and the upper portion thereof in the manner shown diagrammatically in the drawing. A plurality of cyclone separators 30 may be maintained in series, or in parallel, in the upper portion of preheater 3. In the arrangement shown the cyclones are connected by lines 3l to a common header 32 which communicates with line 29. The gas in the upper part of preheater 3 passes into the inlets 33 of cyclones 30, deposits all or a substantial proportion of the entrained solids therein and passes out of the system through lines 3l and 29. The separated solids pass from cyclones 30 through lines 34 to a header 35 from which the returned solids pass downwardly through line 3S to a point substantially below interface I0. A shield 3l may be placed around the lower end of line 35 to minimize the passage of gases into the open end of line 3B.

The provision of solids recovery means in combination with preheater 3 is advantageous in that it minimizes for the whole system the loss r of solids. Furthermore, preheater 3 represents the only place in the system in which the gas temperature is sufficiently low to make practicable the application of recovery means, such as cyclones. Ordinarily this reduires that the temperature be not substantially higher than 1000" F.

The solids which are carried out of reactors I and 2 and economizer 4 by entrainment in the gas streams passing overhead are recovered in the succeeding chamber to which the exit gas stream passes. Thus solids carried overhead by entrainment through line are recovered in preheater 3 and returned to reactor 2 through standpipe 9. Also solids entrained in the gas stream in line I I are recovered in reactor 2 and returned to reactor I through standpipe I5. In a similar manner solids carried overhead from economizer 4 through lines I9 and 25 are recovered in reactor I and in reactor 2 and returned through standpipes 20 and I5, respectively.

The pressure on the system need be no higher than the pressure necessary to pass the gas stream through the system plus the pressure necessary at 29 to dispose of the waste gas. The pressurel at which the air is supplied through line yabout 1.5 feet per second and an 23 may be in the order of 37 pounds gage which is suiricient to uidize the solids in the four chambers, pass solids through the system and pass the waste gas out through line 29 at a pressure somewhat above atmospheric.

The temperature in main reactor I is maintained at a substantially uniform level within the range of 2000-2650 F. In accordance with a preferred modiiication of this invention the main reactor is maintained at a temperature below the temperature at which fusion of the solids would occur or in the range of 200G-2450" F. The maximum temperature permissible without substantial fusion is most desirable.

The temperature in carbonate reactor 2 is maintained at the level necessary to effect rapid conversion of the carbonates such as calcium carbonate to corresponding oxides. For this purpose a temperature of approximately 1050n F. is satisfactory although somewhat lower temperatures may be employed.

The temperatures in preheater 3 and economizer 4 have no bearing on the reaction and are governed entirely by considerations of efficiency in heat saving. Examples of such temperatures will be given in the following example.

An example of the operation of the process described above will be given in the following description of the operation of a plant designed and operated to produce 735 tons per day of a Portland cement comprising a mixture of dicalcium silicate, tri-calcium silicate, tri-calcium aluminate and small amounts of iron oxide, magnesia and other minor ingredients. This material is produced from a raw material consisting essentially of silica, alumina and calcium carbonate and ground suiiciently fine that of the powder will pass through a number sieve. Analysis of this powder is as follows:

Weight per cent Silica 14.0 Alumina and iron oxide 6.7 Calcium carbonate 74.8 Magnesium carbonate 1.2 Combined water 0.6 Miscellaneous 2.7

Total 100.0

This powder has a specic heat, in the range of 60-l650 F., of about 0.25 B. t. u. per F. per pound and has a filling weight of 50 pounds per cubic foot.

The above described feed powder is charged to the system at a temperature of about 60 F. through line 6 at the rate of 95,000 pounds per hour. At the same time 107,000 pounds per hour of gas at 1650 F. is passed through line 5 into preheater 3. The inside diameter of line 5 between line t and preheater 3 is dimensioned with respect to the volume of gas passing therethrough to provide a linear velocity in that part of line 5 of approximately 50 feet per second. The resulting dense bed of charged material in the preheater 3 is thus heated to a temperature of about 850 F. and the waste gas is withdrawn through line 29 at about the same temperature. Preheater 3 has an inside diameter of approximately 25 feet and the dense phase maintained therein occupies about half the volume of that chamber or about 7,360 cubic feet. The gas flow corresponds to a maximum supercial velocity of average density in the dense phase of approximately 22 pounds provideseven distribution-of gap-s flowsandfeftects suicientheat'- exchange withthewwastefgas.

The preheatedffeed` powderfis withdrawn from preheater -3- -through standpipe-#Q atE the Yratef'of 95;000 poundspenhour. #At the "sameitimef/hot gas -from --reactor I --and Aecor-iomizer "4fis passed through line I I into the-bottomiot carbonatefreactor-2y atl the rate ofi-67585- pounds peru hou-riand at a temperature of approximatelyiofll. 'what -part of line i I f through -whichthef-resulting mixture of powder and gas iiowi to reactorfbziisddif mensioned to provide -a velocity 4-of f dori-feetvper second. Carbonate reactorfhasanfi'nsidei di 1 ameter of" 27 feet and f providesa "d'ensevphase depth of approximately- 1-5`f feet; 'f-Thisoccupies A-about one-half? the'l volume outlievearbonateureactor. In carbonate reactor-i2 the reactionitem- `peraturefof v1650" F.' -is maintainedl throughout #by the n'introduction of 5,886-poundsf1peri hour 20 inchof= powderedcoal. i'IYhe oxygen: necessary: tov-support xcombustion is'contained f in-i the-:gas introfduced lthrough line il Il. lThe resulting rinters mediate-product powder-has=aflling :weight-:of Yapproxiniately:t pounds: per]v cubiciootewhereby the average density= -offthev dense phase; infcar'- .'bonate reactor A2V 'isi-about 271. pounds @per cubic foot. The. average'holding. timeffor the-powder '---in reactor 2f-in :accordance with 1 the' conditions outlined above; isE approximately m hours.

The product or' the.- combustion 1 .which takes 1 place f in the dense phasev of thelca'rbonate .re-

aotor, :approximfatel y`'3;000l pounds -per hour, together with thev carbon vdioxideYliberate'd,,.ap-

n, ai.

0 sels-atamaximumsupe eats'the rateforaboutf'ai' tons-perday. Thezfpre- '-,heatedeY air-fisfdivided at. theftop-fof :economiser -4 i-.tosprovidef'the-'volumen-ofiair required for reactor.

I, which flows through line I9, andtheremainder is passed through line to line II and into adm-iasture withthe hotvgasesfrom reactor:v I. 'I-'his amixtureghas :ai-temperature of about 16001"E.

The rforegoing operating conditions involve passing i theigasffstreain :through .fthe-1 various ves- -cialyel-oci-ty of'1;5 feet v'per second'.` fishintroduced throghline-123 at `a pressure ofi' yapproir-irna'tely'P37'pounds. gage lat theexitfof-I compressor 124: As -a--result vof the pressure-drop'sini linel'fZi-ii the pressure. isreduced 1tofila pounds-pensquareinch in the-bottom-of economizeri'l The-pu'essureldropcaused;4 by 'the dense Vbeth-in-eoonornizerd reduces-the pressure -:-to=`25-.7 pounds persquarel inch. "Thepressure-further#declinesI in line :Wto-2224' poundsfper square in thebottomof'f'reactori. "The densebed of reactants-1 inf that chamberflreduces the pressureliiu-rther to abou-telde@ pounds per squares inch in the top of that vessel. Likewisethe pressure is--further--1ecluced== iriel-ii-ie'4 I Iwtoa pressurel of` 10,8 pounds perl square `inch fin-- the bottom offearfbonatereactor-2l andi-thisl is'ffurth-er v.reducedto -the'f-topl=oftthatwreactor- In .preatey thepressurein the'flooti;ox'n ofthe vessel 1. is about '-4f7fpounds per :square r. inch: 4ands at.` :the entran-coeur cyolones'iS-U itvisiabout :2:31 pounds per :square inch.

heistandpipesfSf-,iF52, ZIIra-ndfG-.areprovided to etEectftranSenorsolids: fromiafzoneof; lrelatively l'aw f* pressure i im the 1f vessels, fin-Which .the lsen.-

:proximately "34;000 pounds v'peri-hour; are-idis- L335tra-ncsacisti/ie@stanclpipesearelocated to;trnasfer :charged-from carbonate reactorfz't'-li-r.oughy linet.

"The powdered intermediate :productfisewithdrawn from reactor .121- through frstandpipe f that the rate of approximately $13221":poundsuper hour (includinge'll pounds per hour of ash). This powder is picked up in line I 9 by preheated air-`fron1 economiser 4`-fwhich1ffiowsthroughIline I9 at theiratefofpll'noundspeuhour at 1100 F. .That part of line lathr-,ough whichthe re- .sulting mixture passes is,dimensioned `toppro- ,vide aj. linear velocityoiADgfeetvper second; 1Re- .actor I is dimensioned to provide amayerage 4holding, time of approximatey threeihfiurs. Consequently reactor" I has an inner diameter of approximately 16 feet and the dense phase is maintained at a height of approximately 27 feet. In order to maintain a reaction temperature of approximately 2350 F. the heat of reaction must be supplemented. For this purpose '750 pounds of powdered coal per hour are charged to reactor I in any suitable manner to maintain the reaction temperature at the desired level. The fluidized powder in reactor I has an average density in the dense phase of approximately 36 pounds per cubic foot.

The product powder is withdrawn from reactor I through standpipe 20 at the rate of approximately 61,281 pounds per hour (including 531 pounds per hour of ash). This material is passed into line 23 at a temperature of about 2350 F. where it is picked up by air which is supplied by compressor 2t at the rate of 66,895 pounds per hour. This air, which is at a temperature of 220 F., and the product powder are contacted sufficiently in economiser d to preheat the air to a temperature of 1100u F. For this purpose economizer 4 has an inside diameter of 14.5 and the fluid bed height is maintained at approximately 15 feet. The product powder, at a temperature of 1100 F., is withdrawn through standpipe 26 sens-tyfus the.-

v-linesfatfrel-atimirly: high` pressures. *This is `vaccomplished -byfreducingflthefdegree off `aeration vvofithe solidsiin thef.- standpipesfwherebyv the density of theanater-ifa in theestandpiipes isg-greaterf-than the denseilbedtrom-f vhicn it'frecei-ves -itsfpowdera For examplegdaerationf ofwstandpipe f$l is1regulatedftto produce inv the standpipe'f an aireragewdensityoiaboutfEOlpounds."percubicoot. ftmaddition 'standpipeiilf is rovided lWitt-1` al length suohithat the pressure in' theabottom off tin-estand- -pipe 1.=is.suii"1cient to `rovercomethev pressure drop ttl-fnoug-hfvalye tfand provide .a residual pressure :ati the ieieitf-of` the' valizeestui'cienty` toi 1n-eventn the tflow otgasesupwardlyainto:standpipe- Si.l 4For this purpose; ini theapparatus described.:abovefstandpipe 9 is provided with a length of approximately 68 feet. Similarly the density of the powder in standpipe I5 and the length of the standpipe are regulated to provide a pressure of approximately 25.4 pounds per square inch at the exit of valve I8. This corresponds to a powder density in standpipe I5 of about 35 pounds per cubic foot and a length of the standpipe of about 81 feet. Standpipe 2d is provided with a length of about 40 feet and the density of the product powder therein is regulated at about 35 pounds per cubic foot to provide a pressure at the exit of valve 22 of about 33.5 pounds per square inch.

General interior dimensions only are indicated in the drawing but it is to be understood that extensive insulation is required to reduce radiation losses from the system to a minimum. It will be understood furthermore that the construction of the various vessels is necessarily governed by the operating temperatures. Reactors I and 2 are lined with suitable refractory materials to withstand the relatively high temperatures existing in those zones of reaction and it may be desirable also to provide such insulation for economizer 4. Preheater 3 may be con- 15 structed of sheet steel but considerable outside insulation is required for this vessel, and the others, to achieve maximum thermal efiiciency in the system.

claim:

1. A method for controlling the flow `oi powdered solids which includes: downwardly flowing a stream of said solids to form a vertically extended standpipe column; introducing an aerating vapor upwardly through said column of downilowing solids to maintain said column in a turbulent pseudo-liquid state; passing said downiiowing stream of solids through a constantly open zone of xed reduced cross-section at the lower end of said column into a region of substantially lower pressure than the pressure at the lower end of said column; and making all variations in the ow of said solids for substantial periods solely by increasing or reducing the rate of introduction of said aerating vapor to increase or reduce the pressure head across said zone while maintaining said restricted zone at the same reduced cross-section.

2. In a process for contacting powdered solids with a plurality of different gasiform streams inv separate first and second contacting Zones, which process includes separately passing different gasiforrn streams upwardly through the mass of said solids in said separate rst and second contacting zones at such velocities that the solids in each zone are maintained in a iiuidized state and an interface is maintained between a lower dense phase and an upper light phase in each zone, the method for controlling the rate of iiow or solids from said rst contacting zone to said second con-- tacting zone which includes the steps of: downwardly withdrawing a stream of solids from a level below said interface in the iirst of said contacting zones, said downflowing stream forming a vertically extended standpipe column of sufficienti' height and density to develop a pressure at its lower end in excess of that required to transfer solids to said second contacting zone; introducing an aerating vapor upwardly through said column of downlowing solids to maintain said columni in a turbulent uidized state; passing said downfiowing stream of solids through a constantly open zone of fixed reduced cross-section at the lower end of said column into a transfer zone ring solids from said transfer zone into said sec- -ond contacting zone by means of an entraining vapor; and making all variations in the dow of said solids from said rst contacting zone to said second contacting zone for substantial periods solely by varying the rate of aeration of said downflowing stream of solids to increase or reduce the pressure head across said zone while maintaining said restricted zone at the same reduced cross-section.

3. A method as claimed in claim 2 in which cements are formed in said nrst contacting zone and said downowing solids are at temperatures in excess of 2000 F.

4. In the method for contacting powdered solids with a gasiform fluid in a contact zone which includes, maintaining a dense, fluidized, pseudoliquid bed of suspended solids in at least the lower portion of said contact zone, continuously introducing said gasiform fluid into the lower portion of said contact zone and passing said gasiiorm duid upwardly through said dense, fluidized, pseudo-liquid bed, continuously introducing a stream of powdered solids into said dense, fluidized, pseudo-liquid bed and continuously withdrawing from said dense, fluidized, pseudo-liquid bed a downiiowing stream of powdered solids, the method of regulating the downward flow of said last-named stream which comprises, passing said downiiowing stream into a constantly open zone of xed, restricted cross-section, introducing aerating gas into said downfiowing stream above said zone of fixed restricted cross-section and Varying the rate of ow of solids through said zone for substantial periods solely by varying the rate of introduction of said aerating gas to Vary the density of said downflowing stream while maintaining said restricted zone at the same reduced cross-section.

ROBERT PYZEL.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,409,707 Roetheli Oct. 2.2, 1946 2,468,521 Sweetser et al Apr. 26, 1949 2,469,989 Pyzel May i0, 1949 2,529,366 Bauer Nov. 7, 1950 region of substantially lower pressure; transfer- 

